Publications

Electronic components such as bipolar junction transistors (BJTs) are damaged when they are exposed to radiation and, as a result, their performance can significantly degrade. In certain environments the radiation consists of short, high flux pulses of neutrons. Electronics components have traditionally been tested against short neutron pulses in pulsed nuclear reactors. These reactors are becoming less and less available; many of them were shut down permanently in the past few years. Therefore, new methods using radiation sources other than pulsed nuclear reactors needed to be developed. Neutrons affect semiconductors such as Si by causing atomic displacements of Si atoms. The recoiled Si atom creates a collision cascade which leads to displacements in Si. Since heavy ions create similar cascades in Si we can use them to create similar damage to what neutrons create. This LDRD successfully developed a new technique using easily available particle accelerators to provide an alternative to pulsed nuclear reactors to study the displacement damage and subsequent transient annealing that occurs in various transistor devices and potentially qualify them against radiation effects caused by pulsed neutrons.

The effects of photocurrents in nuclear weapons induced by proximal nuclear detonations are well known and remain a serious hostile environment threat for the US stockpile. This report describes the final results of an LDRD study of the physical phenomena underlying prompt photocurrents in microelectronic devices and circuits. The goals of this project were to obtain an improved understanding of these phenomena, and to incorporate improved models of photocurrent effects into simulation codes to assist designers in meeting hostile radiation requirements with minimum build and test cycles. We have also developed a new capability on the ion microbeam accelerator in Sandia's Ion Beam Materials Research Laboratory (the Transient Radiation Microscope, or TRM) to supply ionizing radiation in selected micro-regions of a device. The dose rates achieved in this new facility approach those possible with conventional large-scale dose-rate sources at Sandia such as HERMES III and Saturn. It is now possible to test the physics and models in device physics simulators such as Davinci in ways not previously possible. We found that the physical models in Davinci are well suited to calculating prompt photocurrents in microelectronic devices, and that the TRM can reproduce results from conventional large-scale dose-rate sources in devices where the charge-collection depth is less than the range of the ions used in the TRM.